News Blog

Scientists “Myth Bust” Human VS Animal Competition

July 21, 2017

| by
Abbey Anderson

This time last year the Olympics were in full swing, with all eyes on some of the greatest athletes of our time. We saw the cupping phenomenon in center stage – and on Michael Phelps’ shoulders – we watched Katie Ledecky win four gold medals (and one silver) in as many races, and we heard one swimmer talk about the effects of menstruation on her race, an often taboo subject. While we aren’t watching Olympians set records and break barriers this year, some athletes are still making headlines. On Sunday, Phelps will go head-to-head against a very unlikely competitor: a great white shark.

Yes, you read that correctly – an actual shark.

While the logistics of this race alone leave me with many, many questions, I’m most curious about whether this would even be a fair fight from the get-go.

Man VS Shark

“Sharks have everything going for them when it comes to moving through the water,” said Peter Dodson, BSc, MSc, PhD, a professor of Anatomy at the University Of Pennsylvania School Of Veterinary Medicine. “Their entire body is aerodynamic, as they have lived in and mastered moving through water for their entire existence.”

Dodson described the body of a shark as “hydrofoil,” meaning they move through the water with minimal resistance and their body naturally generates lift as it moves, sort of like airplane wings flying through the air. Dodson added, “Phelps, like all humans, leads with a very bulbous head, whereas the shark is very streamlined – flat at the front and rising to the top at the fin, which helps them cut through the water with very little drag.”

The bulbous head aside, “the best characteristics for any swimmer is their ability to displace water backwards – which is what moves us forward, ” said Brian Sennett, MD, chief of Sports Medicine at Penn Medicine. “In humans, long legs and long arms with large hands make the best "paddles.” Strong muscles in both the legs and the arms and shoulders provide the power to move the water quickly, and a thin body allows the least resistance to flow.”

Sennett went on to note that strong core muscles allow the swimmer to hold a straight shape in the process of swimming. He said, “If the body bends and sags, it results in ‘drag’ or resistance to flow, which slows down the momentum. Specifically for Michael Phelps, his tall, lean, powerful shape with has large feet and hands are his biggest advantage.”

But it may not be enough to compare to his adversary.

“As we move to the back of the animal,” Dodson said, “sharks have a great deal of motion in the tail, which is powered by the muscles in the back quarter of the animal. Rather than much of a human’s power coming from their legs and arms, the shark uses muscles throughout the entire mid-section to power its tails and move forward.”

Sennett echoed this point adding, “the biggest differentiator between the two is power production. The muscular contraction delivered to a stiff fin is ideal in a fish, which is where the shark’s superiority lies.”

In fact, it’s being reported that during the race – which was pre-tapped – Phelps wore a monofin on his feet, which helped him get from his typical speed of about six miles per hour to nearly 12 MPH against the shark – which makes sense according to Sennett and Dodson.

“Propelling a swimmer forward really comes down to displacement of water and pushing that water backwards,” Sennett said. “A fin and tail displace water backward far better than a cupped hand and a non-cupped foot. Combine these advantages with the tapered body, and the shark has a supreme advantage.”

While the deck seems to be stacked in favor of the shark from the beginning – even with Phelps’s added fin and wetsuit – one has to think about some of the more internal differences that may give one competitor a leg – or fin – up.

“The intestinal structure of a shark is much smaller than that if a human’s,” Dodson said. “This means a higher portion of the shark’s body is devoted to muscle mass, whereas a human body needs to have room for a larger intestine and abdominal organs.” And when it comes to breathing, Dodson added, “of course, a shark is going to be better off here, too.”

At a cellular level, sharks and humans process oxygen in relatively the same way, but it’s their intake that really makes the difference.

“In both sharks and humans, oxygen is taken in by lungs (or gills), absorbed into the blood stream, and disseminated to muscles,” Sennett said. “The muscles produce a significantly greater amount of energy when operating with oxygen – the aerobic state – versus without oxygen—anaerobic state.”

One difference, though, is the way humans work to maximize their body’s ability to utilize oxygen. Sennett said, “When elite athletes train, they often measure their “VO2 max”– which stands for volume, oxygen, maximum, an important measure of endurance capacity. VO2 max is reached when the body does not take up any more oxygen in response to increasing exercise. Training at this threshold allows an athlete to exercise at the highest capacity because they’ve trained their body to better absorb oxygen in the lungs, carry oxygen to the muscles, and delivery oxygen to the muscles.”

While humans may be able to train their bodies to work most efficiently, they still have to take in oxygen and expel carbon dioxide with actual effort. Another advantage for the shark is that their gills allow them to continuously take in and process oxygen as they move.

“Phelps is limited by the fact that he has to change his body position to breathe, which causes a resistance to flow, and makes him less hydrodynamic,” Sennett said. “If Phelps were to have used a snorkel, his speed may have been improved a result of being able to stay underwater – although the snorkel itself would cause additional drag or resistance to flow.”

Not only does the mechanism of breathing hinder humans, the actual air they take in gives them a disadvantage as well. “I think what may be the most important breathing difference is the buoyance that comes with lungs versus gills,” Dodson said. “Phelps carries a bubble of air around with him in the water because he has lungs. While normally this is a good thing – for human survival – it does increase the volume in the cross-sectional area that’s passing through the water. In the simplest terms, this buoyancy makes it harder for one to swim when their body is constantly pulling them to the top of the water.”

Man VS Cheetah

While the laws of nature and evolution were in the sharks favor against the greatest Olympian of all time, will that always be the case? There don’t seem to be any plans for Usain Bolt to race a cheetah, but if he were to, could he win? Of course, we may surmise which competitor would come out on top – and some have already attempted to pit the two against one another – but one has to figure that these two creatures, both of who live and run on land, must have more similarities than humans and sharks.

“The factors that relate to speed are length of a stride, cadence (pace) of the stride, and resistance to air – again, the aerodynamics,” Sennett explained. “Unfortunately, Usain Bolt has the disadvantage with respect to stride length and aerodynamics.”

We can all assume, most obviously, that four legs are better than two – and Dodson agrees. He said, “humans have long legs, which are very good for walking and running long distances, but not for running at top speed. But the biggest advantage for the cheetah is its spine.”

“The lower back of a cheetah is very flexible and the animal’s most powerful muscles are in the lumbar region of the spine,” Dodson said. “As the cheetah moves, the whole body flexes and extends – it bends down and back up – to coordinate the running movements. Extending that motion is the flexibility of the shoulder blades, which are very mobile, allowing the forelimbs to swing back and forth as it runs, lengthening the stride of the animal.”

This ultimately allows the cheetah to cover more ground with one stride. Even though a human’s legs are longer, when the cheetah’s fore and hind limbs are both extended mid-stride, it far exceeds the length of the human stride.

Another advantage is associated, again, with the back. Dodson explained, “A human needs to engage specific muscles to keep itself upright and to maintain proper posture. Since a cheetah does not stand up tall, a majority of its muscles can be actively engaged in the act of running.”

On a positive note for us humans, as Sennett explained previously, Bolt has a disadvantage when it comes to stride length and aerodynamics, but humans – at least those as fast a Bolt – may have be superior when it comes to cadence.

“When Bolt ran then 100 meters in 9.58 seconds, his cadence – how quickly he turned strides – was measured at 4.28 strides per second,” Sennett said. “A cheetah on the other hand, while being able to cover 100 meters in 5.95 seconds, measured 2.4 strides per second. But, as the cheetah reaches a higher speed – as high as 70 MPH compared to Bolts 28 – its cadence increased to 3.5 strides per second.”

As Dodson and Sennett described, the cheetah still defeats human’s stride length, proving, once again, human versus shark or cheetah is no competition. And as Sennett so frankly pointed out, a human could just as easily be defeated by these two simply by being eaten.

For Susan Weiss, PhD, a professor of Microbiology at the Perelman School of Medicine with more than four decades of experience studying coronaviruses, the pandemic means more work for her, and her students, post-docs, and technicians, than ever before.

University of Pennsylvania Perelman School of Medicine scientists and clinicians have begun an unprecedented number of studies and clinical trials investigating a single virus, SARS-CoV-2, and COVID-19, the disease it causes.

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